53] THE SKULL OF AMIURUS— KINDRED 53 



ments entering into its composition. In the ganoids (Van Wijhe, 1882) there 

 is a dermopalatine below the perichondria! autopalatine which, in Spatularia 

 (Polyodon), is attached to the maxillary and in Polypterus to the ectoptery- 

 goid. No such bone or ossification occurs in Amiurus. 



The pterygoquadrate cartilage is larger than in the younger stage and the 

 pterygoid part forms the middle of an osseous sheet, which extends ventrally 

 beneath the cranium and posteriorly below, medial to Meckel's cartilage (Fig. 

 5). This is the centre of the metapterygoid bone of the adult. The quadrate is 

 ossified along its ventral margin and is continuous dorsally with the ossification 

 around the ventral and anterior edges of the hyomandibular cartilage. The 

 posterior edge of this ossification is raised slightly above the surrounding parts 

 and encloses the superior part of the operculo-mandibular canal of the lateral 

 line; it is the anlage of the preopercular bone which has these relations in the 

 adult. The hyomandibular branch of the facialis issues through this ossifica- 

 tion, immediately below the anterior edge of the hyomandibular cartilage. 

 This whole region, except for the preopercular part, was prefonrxcd in cartilage 

 in the younger stage, the latter part having become secondarily attached to the 

 perichondria! ossification of the hyomandibular. The dorsal part of the hyo- 

 mandibular cartilage persists and abuts against the lateral surface of the otic 

 capsule in the same region as in the younger stage. The opercular knob on its 

 posterior face is larger and furnishes articulation for the thin p'ate-like 

 operculum (Fig. 5). The interoperculum lies at the ventral end of the latter, 

 between it and the mandible. 



The centre of the dentary bone appears on the lateral surface of Meckel's 

 cartilage and at this stage is distinct from the cartilage (Fig. 25). Teeth are 

 attached to the dorsal anterior surface of this ossification (Fig. 5). A lateral 

 line ossification, v/hich has arisen independently around the mandibular lateral 

 line canal, is attached to its ventral surface and is perforated for passage of 

 dermal tubules of the canal. Meckel's cartilage lies in a groove on the medial 

 surface of this ossification. In the 60 mm. stage perichondria! ossification has 

 appeared on the surface of the cartilage and is connected by osseous trabeculae 

 with the dermodentary (Fig. 24) . The cartilage at the anterior end of the jaw has 

 been resorbed where the symphysis takes place and the ossification here, 

 although usually fused with the dentary, has been compared by Van Wijhe to 

 the mento-Meckelian bone in the ganoids. He says (1882) that this bone is dis- 

 tinct in Polypterus and Amia and that itls fused with the dentary in Lepidosteus. 

 The dentary is present as a dermal bone only, in all of these forms. In Salmo 

 (Schleip 1903) the dentary is made up of the same elements as in Amiurus. 

 McMurrich (1884b) recognized the elements which make up this bone in 

 Amiurus. 



The posterior end of Meckel's cartilage is covered by a perichondrial ossi- 

 fication, the centre of the articulare, which furnishes the surface for articula- 

 tion with the quadrate. There is no independent ossification on the top of the 



